Two Caenorhabditis elegans actin depolymerizing factor/cofilin proteins, encoded by the unc-60 gene, differentially regulate actin filament dynamics.
The Caenorhabditis elegans unc-60 gene encodes two actin depolymerizing factor/cofilin proteins which are implicated in the regulation of actin filament assembly in body wall muscle. We examined the interaction of recombinant UNC-60A and B proteins with actin and found that they differentially regulate actin filament dynamics. Co-pelleting assays with F-actin showed that UNC-60A depolymerized but did not remain bound to F-actin, whereas UNC-60B bound to but did not depolymerize F-actin. In the pH range of 6.8-8.0, the apparent activities of UNC-60A and B did not change although UNC-60A showed greater actin-depolymerizing activity at higher pH. These activities were further confirmed by a light scattering assay and electron microscopy. The effects of these proteins on actin polymerization were quite different. UNC-60A inhibited polymerization in a concentration-dependent manner. On the other hand, UNC-60B strongly inhibited the nucleation process but accelerated the following elongation step. However, an excess amount of UNC-60B increased the amount of unpolymerized actin. These results indicate that UNC-60A depolymerizes actin filaments and inhibits actin polymerization, whereas UNC-60B strongly binds to F-actin without depolymerizing it and, through binding to G-actin, changes the rate of actin polymerization depending on the UNC-60B:actin ratio. These data suggest that the two UNC-60 isoforms play differential roles in regulating actin filament dynamics in vivo.
Ono
S
S
Departments of Pathology and Cell Biology, Emory University, Atlanta, Georgia 30322, USA. ono@bimcore.emory.edu
Benian
G M
GM
D051339:Actin Depolymerizing Factors; D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D001704:Biopolymers; D017173:Caenorhabditis elegans / Q000235:genetics*; D051345:Destrin; D008840:Microfilament Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010710:Phosphates / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
D051339:Actin Depolymerizing Factors; D000199:Actins; D001704:Biopolymers; D051345:Destrin; D008840:Microfilament Proteins; D010710:Phosphates; D011994:Recombinant Proteins